June 6, 2013

The Sun Was A ‘Feisty’ Character In Its Younger Days

Astronomers said during a press conference at a meeting of the American Astronomical Society that when our Sun was in its infancy, it was active and "feisty."

The team said that when the Sun was young it was growing in fits and burping out bursts of X-rays. They came to this conclusion after studying another young star in our galaxy known as TW Hydrae, which sits about 190 light-years away in the southern constellation Hydra the Water Snake.

"By studying TW Hydrae, we can watch what happened to our Sun when it was a toddler," said Nancy Brickhouse of the Harvard-Smithsonian Center for Astrophysics (CfA).

This star is an orange, K star weighing about 80 percent as much as our Sun. It is about 10 million years old and still accreting gas from a surrounding disk of material. Scientists believe this disk may also contain newborn planets.

As a star grows, it "eats" infalling gas from the disk that gets funneled along magnetic field lines to the star's poles. Due to the Earth's angle of this star, astronomers are able to study this accretion process in detail.

As infalling material smashes into the star, it creates a shock wave and heats the accreting gas to temperatures greater than 5 million degrees Fahrenheit. The gas glows with high-energy X-rays and continues moving inward until it cools and its glow shifts to optical wavelengths of light.

"By gathering data in multiple wavelengths we followed the gas all the way down. We traced the whole accretion process for the first time," explained Brickhouse.

The researchers found that accretion was clumpy and episodic in building a star, and at one point the amount of material landing on the star changed by a factor of five over the course of a few days.

"The accretion process changes from night to night. Things are happening all the time," stated Andrea Dupree, also of the CfA.

Some of the infalling material is pushed away in a stellar wind much like the solar wind that fills our Solar System. Some gets channeled into giant loops and stellar prominences. Astronomers have known that young stars are more magnetically active than our Sun, but now they can actually probe the interplay between the star's magnetic fields and the protoplanetary disk.

"The very process of accretion is driving magnetic activity on TW Hydrae," added Brickhouse.

In January astronomers reported in the journal Nature that they determined the mass of the planetary nursery surrounding TW Hydrae. The team said the star's disk had a much larger mass than previous thought, meaning the system is forming planets similar to those found in our Solar System.